Metallurgy of tin



March 1927' E. A. c. SMITH METALLURGY OF TIN Filed June 27, 1925 C/rc'u/a flan 4 J P P @2212 r 2 B/ and 6b (emenfaf/bn.

Anode Secondary l Secondary (e/Z Leach.

Caffiade Ce// /3 4 W D Gu WM wu @ATTORNEYS INVENTOR Patented Mar. 3, Th2? I ELIAS ANTHON CAPIPELEN SMITH, OF NEW YORK, N. 3., ASSIGNOR TO GUGGENHEIM BROTHERS, OF NEW YORK, N. Y., A COPARTNEBSHIP. I

METALLURGY 01E TIN.

Application filed June 27, 1925. Serial No. $0,096.

This invention relates to the recovery of tin from ores, concentrates and other materials in which the tin has been reduced to a metallic condition, and particularly to a cyclical method wherein the tin is leached from materials containing it and separated thereafter by electrolysis with regeneration of .the leaching solution.

The metallurgy of tin as conducted heretofore requires concentration of the ore until it contains from sixty to sixty-five per cent. of tin before smelting is possible economically. In preparing concentrates containing tin in suchhigh proportions twenty to thirtyfive per cent. of the tin is lost in the tailings. This loss, which has been unavoidable here tofore, increases the cost of the recovered tin to a very material extent, but it has not been possible heretofore to avoid this loss because no methods have been available whereby the tin could be separated and recovered economically from low grade materials.

It is the object of the present invention to provide a relatively inexpensive and easily workable method whereby the ore or concentrates therefrom or other material containing tin even in relatively small proportions can be treated to recover the tin there from, and incidentally to separate it from impulrities which are present in the raw ma- Other objects and advantages of the invention will be apparent as it is better understood by reference to the following specification in which the preferred embodiments of the invention are descfibed. i

In carrying out the invention it is essential that the tin or at least a portion thereof be reduced to the metallic form in the ore, con centrates or other tin-bearing material since the method herein described is not desi ed primarily to separate compounds of tin om the raw material. The reductionmay be car ried out in any usual or desired manner as, for example, by heating the tin-bearing material in the presence of agaseous reducing agent. It is essential also that the tin-bearin material shall not besinteredto any su )stantial extent because i the sin'tering would interfere with the subsequent leaching operation. The material delivered to the leaching plant should be in a. granular condition, that is to say, in the physical form in which it comes from the crushing plant or concentrating mill. The reduction may be carried to a greater or less extent but as much as possible of the tin should be re duced since only metallic tin is dissolved in the primary process. It is possible, however, to separate tin sulphide from the raw material by a supplemental method hereinafter described.

The invention depends upon leaching the material containing reduced tin with a solvent which is capable of dissolving the tin. One example of a suitable solvent is a solution containing from twenty to twentyfive grams per liter of tin in the form of stannic chloride, one hundred grams per liter of iron in the form of ferrous chloride and twenty-five grams per liter of acid. Hydrochloric or sulphuric acids are preferred because these are relatively inexpensive and easily obtainable. The proportions of the several ingredients are those which in a particular instance gave the best results, but it is not essential that the proportions be adhered to strictly, and variations will occur in the operation of the method Without affecting the results obtained to a serious extent.

'Tn leaching an ore relatively free from acid soluble iron the iron content of the solution may decrease considerably below that of the example, for, as hereinafter explained, it is chiefly in leaching the less soluble forms of tin such as tin sulphide that the presence of value. I v

Likewise the limits of acid and tin coniron becomes of particular centration in the leaching solution may vary considerably, higher acid concentration sometimes being carried to makeup for larger losses in the leaching operation and higher or lower stannic tin concentrations being carried depending on the ease of dissolution of the tin mineral and the concentration of tin desired infthe solution going. to the volume of leach solution and the less volume of solution that must be employed to leach the ore.

This invention will be better understood by reference to the flow sheet shown in the accompanying drawing, taken in conjunction with the following description:

The reduced tin-bearing material to be leached is held in an appropriate container 1 in contact with the leaching liquor. In practice, these materials are suitably agitated and the resulting solution passes through a line '2 to primary cells 3 where tin -is electrodeposited. In cells 3 the leaching liquor is regenerated and a portion of it is returned through a line 4 to the primary leach 1. In practice, in order to facilitate the operation of the rimary cells 3, part of the electrolyte is addltionally circulated through the cells 3 and a line 5.

The residue from the primary leach (1) contains such materials as antimony, bismuth, tin sulphides, etc., which are removed in a suitable manner from container 1 through a line 6 to a secondary leach in container 7 The leaching solution for the secondary leach is derived from the primary leach solution. Part of the primary leach liquor is withdrawn from cells 3- through a line 8 and subjected to electrolysis in an ordinary cell 9 of the diaphragm type which is resistant to acid corrosion. The electrolysis results in the deposition of some tin and the regeneration of solution containing ferric chloride. The solution is then returned through a line 10 to the primary cells 3 and part of this solution is returned to the anode compartment of cell 9 through a line 11.

From the anode compartment of the secondary cell 9 the ferric chloride leach solution passes through a line 12 to the secondary leach container 7. Here the ferric chloride dissolves the antimony, bismuth and tin sulphides. The tailings, substantially free from tin, antimony and bismuth are discharged from the container 7 through an outlet 13.

The regnant solution from the secondary leach 7) is returned to the primary leach 1) through a line 14. In practice, part of the solution flowing from the container 7 is by passed through a line 15 to a container 16 where the bismuth and antimony are cemented out on tin metal. The solution from container 16, free from antimony and bismuth, is returned toa line 14 through a line 17, from whence it passes to the primary leach 1.

Acid additions to the solutions can be made using either hydrochloric or sulphuric acid. Since sulphuric acid is as a rule much cheaper than hydrochloric acid this is the acid preferred. In this case it is usually desirable from time to time to add to the solution quantities of. some appropriate chloride so as to maintamzachlorideconcentratlon in the solution of 10 grams per liter or over. The chloride has a number of advantages in promoting dissolution and eliminating hydrolysis of the tin as Well as in some cases tending to give a more perfect and adherent tin deposit in the electrol sis.

Another particular a vantage in using leach solution of the above character is embodied in its remaining an efficient leaching and electrolytic solution even after building up to saturation in ferrous iron. By carrying the iron in the solution at its full saturation value the necessity of discarding solution because of continued dissolution and contamination from iron compounds in the ore being leached is avoided. The iron sulphate builds up in the solution to a saturation value and thereafter any further iron dissolve-d from the ore precipitates again,-

either in the ore itself or subsequently.

The action of the solvent may be indicated as follows:

and if any ferric chloride is present it will react as follows:

Sn-l-QFeCh:SnCh-l-EZFeCl The leaching may be carried out by..percolation or agitation in any suitable container which is capable of holding the solvent. The mechanical features of the leaching equipment may be varied in accordance with Well understood practice and do not affect the result which obviously is to dissolve the tin which is present in the raw material. The tin appears as stannous chloride in the solution which is delivered from the leaching plant. This solution will contain, for example, forty grams per liter of stannous chloride, one hundred grams per liter of ferrous chloride and fifty grams per liter of acid. The roportion of stannous chloride in the solutlon from the leaching plant will vary, of course, depending upon the practice followed, but it is preferable to so proportion the volume of solutionused to the amount of tin present in the raw material that a solution containing about forty grams per liter of stannous chloride Will be obtained.

The solution from the leaching plant is delivered to the electrolytic cells wherein the t1n is separated. These cells may be of any of the well known types without diaphragms and provided with cathode plates of tin or other suitable metal. The anodes may be of graphite or any other corrosion-resistant anode material. The electrolyte is supplied continuously to the cells while curent is permitted to flow therethrough with the result that tin is deposited upon the cathode. The

the ferric chloride immediately into ferrous chloride. The reactions may be indicated as follows:

Consequently the solution leaving the cells will contain stannic chloride, ferrous chloride and acid. and if properly regulated the operation will result in the production of a solution containing from twenty to twentytiv'e grams per liter of stannie chloride, one hundred grams per liter of ferrous chloride and fifty grams per liter of acid. This, it will be noted, is the solution used originally in leaching the raw material, and consequently it can be returned to the leaching plant for the treatment of additional material. The net result of the operation is to dissolve approximately twenty grams of tinper liter of solution used from the raw material and to deposit it upon the cathode.

The ferrous chloride in the solution plays no part in the leaching operation,- but in the electrolysis it acts as a depolarizer to reduce the cell voltage of 3.0 volts to 1.4 volts. The acid is used to prevent hydrolysis of the iron and tin chlorides and the proportion mentioned is high enough for that purpose, yet not suificiently high to dissolve the cathode to any serious extent.

Whileit is not essential, it is preferable to employ a small amount of a colloid addition agent in 't-he solution of electrolysis for the purpose of improving the character of the deposit at the cathode. Usually there is a suflicient amount of silicic acid derived from the ore or concentrate so that no extraneous material need be employed. However, the cathode deposit can be improved by the addition of a small amount of Inc to the solution, particularly if it is deficient in silicic acid.

The method as described relates to the treatment particularly of materials containing tin in a metallic statel In practice, however, the-reduced material will often carry as much as ten per cent of tin in the form of sulphide and thesulphide is not dissolved readily by stannic chloride. It isrefractory also to most leaching agents. Consequently the tin sulphide, if present in the raw material, will be mostly left therein at the end of the leaching operation and will remain in the residue or tailings. My experiments have shown that it ispossible and economical to leach the sulphide from the residue by the application of amodified method using a solution containing ferric chloride. The reaction is indicated as follows:

The solution can be derived from the soluelectrol sis. -\Vhen such a solution is electrolyze in a diaphragm cell ferric chloride is formed with high current efficiency. It can be produced also by passing chlorine gas into the required leach solution containing ferrous chloride. The solution as-t'hus modilied will contain, for example, twenty grams per liter of stannic chloride, sixty grams per liter of ferric chloride, forty grains per liter of ferrous chloride and fifty grams per liter of acid. This solution can be applied to the tailings from the previously leached material or to fresh raw material containing a large proportion of tin sulphide. The leaching can be carried on by percolation or agitation in accordance with well understood principles and will result in a solution con-- taining, for example, fifty grams per liter of stannic chloride, one hundred grams per liter of ferrous chloride and fifty grams per liter of acid. This solution is subjected to electrolysis in an ordinary cell of the diaphragm type which is resistant to acid corrosion. Preferably it is diluted before it enters the cell by the addition of solution from the anode compartments thereof until the concentration in tin is reduced to about twenty-five grams per liter. The electrolysis results in the den sition of about five grams per liter of tin .mm the solution and the regeneration of the c-Eution containing ferric chloride which was user? as a solvent.

In carrying out the electrolysis some of the spent electrolyte from the cathode compartment is returned to the head cells to.

dilute the incoming solution from the leaching plant for the purpose hereinbefore noted. Theremainder of the spent electrolyte from the cathode compartment flows through the anode compartments where the ferrous iron is oxidized to ferric iron, thus completing the cycle to produce the leaching solution.

As in the electrolysis as first described, it is desirable to have a colloid addition agent present, and unless there is suflicient silicic acid derived from the raw material it is desirable, though not essential, to add a small proportion of glue to the solution. This improvesthe quality of the cathode deposit. a a 1;

An important featureof the method is that impurities present in the raw material such as iron, bismuth, arsenic, antimony, etc., remain therein during the initial leaching to separate metallic tin. Iron, if reduced to the metallic state or to the state of ferrous oxide, is solublein the acid of the leach solution. However, as iron is one of the chief constituents of. the solution, it may be carried at comparatively high concentrations and separated as crystallized ferrous chloride or sulphate, or a portion of the solution can be discarded from time to time to lower the iron concentration.

Metals such as bismuth and antimony are below tin in the electro-chemical series and will not dissolve in the stannic chloride leach solution so long as any appreciable amount of metallic tin is present. Consequently by suit-ably controlling the operation, for example, by withdrawing the leaching solution when the metallic tin has been dissolved, bismuth and antimony will be retained in the residue or tailings with any tin sulphide if the latter is present. Bismuth and antimony are soluble in the ferric chloride leach and will be dissolved, therefore, when the residue is treated for the recovery of tin sulphide. The solution derived from the leaching of metallic tin is thus purified automatically and the tin deposited therefrom will be free from deleterious impurities.

When bismuth and antimony are present in the raw material and are recovered in the ferric chloride, leach, the solution can be electrolyzed and returned for further use until the concentration of antimony and bismuth is sufficiently high to permit recovery thereof by cementation on tin. Thus the ferric chloride solution from the electrolytic cells can be withdrawn at intervals and permitted to percolate over or otherwise contact with metallic tin, and the bismuth and antimony can be removed thus from the solution.

Since the solutions employed are regenerated continuously in conducting the operation, the cost of reagents for use therein is lowered materially. It is necessary only to add sufl icient acid from time to time to maintain the necessary proportion thereof in the solution. Ferrous and ferric chloride arederived from the raw materials treated and the tin, of course, passes from the raw material through the solution to the cathode of the electrolytic cell. The method as described requires no complicated or unusual apparatus, and since only the acid need be transported to the place where the operation is conducted, the method is very economical. Moreover, only a relatively small amount of acid is required to make up for unavoidable losses in the solution.

Various changes may be made in the de tails of the operation and particularly in the proportions of the ingredients present in the solutions used without departing from the invention or sacrificing the advantages thereof.

I claim 1. The method of recovering tin from materials containing it, which comprises leaching the material with mixed solvents containing tin and iron compounds and acids, and electrolyzing the solution to deposit a portion of the tin therefrom and to regenerate the solvent.

2. The method of recovering tin from materials containing it, which comprises leaching the material with mixed solvents containing tin and iron compounds and acids which do not dissolve bismuth and antimony, electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent and recovering bismuth and antimony from the residue left by the solvent.

3. The method of recovering tin from materials containing it, which comprises reducing tin in the material to the metallic state, leaching the reduced tin from the material with mixed solvents containing tin and ferrous iron compounds and acids, and electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent.

4. The method of recovering tin from materials containing it, which comprises reducing tin in the material to the metallic state, leaching the reduced tin from the material with mixed solvents containing tin and ferrous iron compounds and acids, electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent further electrolyzing the solvent forming ferric iron, leaching the residue. with the electrolyzed solvent containing a ferric iron compound and electrolyzing the second solution to deposit a portion of the tin and to regenerate the solvent.

5. The method of recovering tin from materials containing it, which comprises reducing tin in the material to the metallic state, leaching the reduced tin from the material with a mixed solvent containing a stannic salt, a ferrous salt and acids, and electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent.

6. The method of recovering tin from materials containing it, which comprises reducing tin in the material to the metallic state, leaching the reduced tin from the material with mixed solvents containing a stannic salt, a ferrous salt and acids, electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent, further electrolyzing the solvent forming ferric iron, leaching the residue with the electrolyzed solvent containing a stannic salt, a ferric salt and acids, and electrolyzing the second solution to deposit a portion of the tin and to regenerate the solvent.

7. The method of recovering tin from ma terials containing it, which comprises reducing tin in the material to the metallic state, leaching the reduced tin from the material with mixed solvents containing a stannic salt, a ferrous salt and acids, electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent, further electrolyzing the solvent forming ferric acid,

leaching the residue with the electrolyzed solvent containing a stannic salt, a ferric salt and acids, separating antnnony and b1s muth from the second solution by cementation on tin and electrolyzing the second solution to deposit a portion of the tin and to regenerate thesolvent.

8. The method of separating tin from materials containing it in the form of sulphide of tin, which comprises leaching the material with mixed solvents containing a stannic salt, a ferric salt and acids, and electro lyzing the solution to deposit a portion of the tin and to regenerate the solvent.

9. The method of separating tin from materials containing it in the form of sulphide of tin, which comprises leaching the material with mixed solvents containing a stannic salt, a ferric salt and acids, separating antimony and bismuth from the solution by ceme ntation on tin and electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent.

10. The method of separating tin from materials containing it, which comprises leaching successive portions of the material with mixed solvents containing tin and iron compounds and acids, and regenerating the solvent by electrolysis whereby a portion of the tin therein is deposited.

11. The method of separating tin from compounds containing it, which comprises subjecting successive portions of the material having tin in the metallic state to a mixed solvent containing a stannic salt and a depolarizing agent, and regenerating the solvent by electrolysis whereby a portion of the tin therein is deposited.

12. The method of separating tin from compounds containing it, which comprises subjecting successive portions of the material having tin in the metallic state to a mixed solvent containing a stannic salt, a depolarizing agent and acids, and regenerating the solvent by electrolysis whereby a portion of the tin therein is deposited.

13. The method of separating tin from compounds containing it, which comprises subjecting successive portions of the material having tin in the metallic state to a mixed solvent containing a stannic salt and a depolarizing agent, regenerating the solvent by electrolysis whereby a portion of the tin therein is deposited, separating tin sulphide from the residue'by leaching with a mixed solvent containing a ferric salt, and regenerating the second solvent by electrolysis whereby-a portion of the tin therein is deposited.

ifhThe method of separating tin from compounds containing it, which comprises subjecting successive portions of the material having tin in the metallic state to a mixed solvent containing a stannic salt and a depolarizing agent, regenerating the solvent by electrolysis whereby a portion of the tin therein is deposited, separated tin sulphide from the residue by leaching with a mixed solvent containing a ferric salt, separating antimony and bismuth from the second solution by cementation on tin and regenerating the second solvent by electrolysis whereby a portion of the tin therein is deposited.

15. In the cyclical leaching oftln ores and the like, the method of eliminating excess iron reacted with chemically by the constituents of the leach solution which constitutes maintaining the solution at a substantially saturated value of the combined form of iron least soluble in the leaching solutions employed.

16. A solvent solution suitable for leaching'tin ores containing iron comprising a solution saturated with respect to ferrous sulphate and containing appropriate amounts of ferric iron, sulphuric acid and chloride ion.

17. The method of recovering tin from materials containing it which comprises leaching the material with a mixed solvent containing tin and iron compounds and sulphuric acid, and electrolyzing the solution to deposit a portion of the tin therefrom and to regenerate the solvent.

18. The method of recovering tin from materials containing it which comprises leaching the material with a mixed solvent containing tin and iron compounds and sulphuric acid which does not .dissolve bismuth and antimony, electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent and recovering bismuth and antimony from the residue left by the solvent.

19. The method of recovering tin from materials containing it, which comprises reducing tin in the material to the metallic state, caching the reduced tin from the ma terial with a mixed solvent containing tin and ferrous iron compounds and sulphuric acid, and electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent.

20. The method of recovering tin from materials containing it, which comprises re ducing tin in the material to the metallic state, leaching the reduced tin from the material with ,a mixed solvent containing a stannic salt, a ferrous salt and sulphuric acid, and electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent.

21. The method of recovering tin from materials containing it, which comprises reducing tin in the material to a metallic state, leaching the reduced tin from the material with a mixed solvent containing a stannic salt, ferrous salt and sulphuric acid, electrolyzing the solution to deposit a portion of the tin and to regenerate the solvent, leaching the residue with a similar solvent contaming a stannic salt, a ferric salt and an acid, separating antimony and bismuth from the second solution by cementation on tin and electrolyzing the second solution to deposit a portion of the tin and to regenerate the solvent.

22. The method of recovering tin from materials containing it, which comprises reducing tin in the material to a metallic state, leaching the reduced tin from the material with a mixed solvent containing a stannic salt, a ferrous salt and sulphuric acid, oxidizing the ferrous salt in the solution with chlorine to generate ferric salt, leaching the residue with the solvent containing a stannic salt, a ferric salt and an acid, separating antimony and bismuth from the second solution by cementation on tin and electrolyzing the second solution to deposit a portion of the tin and to regenerate the solvent.

23. The method of separating tin from materials containing it in the form of sulphide of tin, which comprises leaching the material with a mixed solvent containing a stannic salt, a ferric salt and sulphuric acid, and electrolyzing the solution to deposit a portion of the tin and regenerating the solvent.

In testimony whereof I afiix my signature.

ELIAS ANTHON CAPPE LEN SMITH. 

